1. Field of the Invention
The present invention relates generally to a substrate holding case for storing or carrying a substrate such as a photomask or a photomask blank for use in the production of semiconductor elements or liquid crystal display elements, and more particularly is directed to a substrate holding case capable of holding various types of substrates having different sizes, and specifically capable of storage or carriage of a photomask with a pellicle.
2. Description of Related Arts
Typical substrate holding cases have been hitherto disclosed in Japanese Utility Model Laid-open Publication Nos. (1) 59-74726 and (2) 63-92788. The former (1) describes a structure where a cushioning material such as silicone rubber is interposed between a mask and covers, while the latter (2) describes a structure using as a cushioning member an elastic material fitted into an inside groove of the top cover. By the provision of the cushioning member, these substrate holding cases have contrived to restrain generation of dust which may be caused by vibration of the photomask. These cases are designed to accommodate a multiplicity of photomasks, and it has been found difficult after all to entirely suppress the vibration of all the photomasks. Furthermore, the structure of the case is large and complicated, and cleaning of the case itself also entails a problem. Furthermore no measures have been made to hold various substrates having different thicknesses or sizes, either. Photomask cases for storing a single substrate are disclosed in U.S. Pat. Nos. 4,511,038 and 4,830,182. Those cases are inconveniently incapable of holding various types of photomasks having different sizes.
With the miniaturization of the photomasks in recent years, however, there has been an increasing demand for a variety of dimensions of the mask. Accordingly, the cases for holding a substrate such as a photomask are also being subjected to a demand for lowered dust generating characteristics and for a capability of holding masks of a variety of dimensions.